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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/sched/sysctl.h>
 24 #include <linux/uaccess.h>
 25 
 26 #include <asm/cacheflush.h>
 27 #include <asm/tlbflush.h>
 28 
 29 #include "internal.h"
 30 
 31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 32 {
 33         pgd_t *pgd;
 34         pud_t *pud;
 35         pmd_t *pmd;
 36 
 37         pgd = pgd_offset(mm, addr);
 38         if (pgd_none_or_clear_bad(pgd))
 39                 return NULL;
 40 
 41         pud = pud_offset(pgd, addr);
 42         if (pud_none_or_clear_bad(pud))
 43                 return NULL;
 44 
 45         pmd = pmd_offset(pud, addr);
 46         if (pmd_none(*pmd))
 47                 return NULL;
 48 
 49         return pmd;
 50 }
 51 
 52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 53                             unsigned long addr)
 54 {
 55         pgd_t *pgd;
 56         pud_t *pud;
 57         pmd_t *pmd;
 58 
 59         pgd = pgd_offset(mm, addr);
 60         pud = pud_alloc(mm, pgd, addr);
 61         if (!pud)
 62                 return NULL;
 63 
 64         pmd = pmd_alloc(mm, pud, addr);
 65         if (!pmd)
 66                 return NULL;
 67 
 68         VM_BUG_ON(pmd_trans_huge(*pmd));
 69 
 70         return pmd;
 71 }
 72 
 73 static pte_t move_soft_dirty_pte(pte_t pte)
 74 {
 75         /*
 76          * Set soft dirty bit so we can notice
 77          * in userspace the ptes were moved.
 78          */
 79 #ifdef CONFIG_MEM_SOFT_DIRTY
 80         if (pte_present(pte))
 81                 pte = pte_mksoft_dirty(pte);
 82         else if (is_swap_pte(pte))
 83                 pte = pte_swp_mksoft_dirty(pte);
 84         else if (pte_file(pte))
 85                 pte = pte_file_mksoft_dirty(pte);
 86 #endif
 87         return pte;
 88 }
 89 
 90 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 91                 unsigned long old_addr, unsigned long old_end,
 92                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 93                 unsigned long new_addr, bool need_rmap_locks)
 94 {
 95         struct address_space *mapping = NULL;
 96         struct anon_vma *anon_vma = NULL;
 97         struct mm_struct *mm = vma->vm_mm;
 98         pte_t *old_pte, *new_pte, pte;
 99         spinlock_t *old_ptl, *new_ptl;
100 
101         /*
102          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
103          * locks to ensure that rmap will always observe either the old or the
104          * new ptes. This is the easiest way to avoid races with
105          * truncate_pagecache(), page migration, etc...
106          *
107          * When need_rmap_locks is false, we use other ways to avoid
108          * such races:
109          *
110          * - During exec() shift_arg_pages(), we use a specially tagged vma
111          *   which rmap call sites look for using is_vma_temporary_stack().
112          *
113          * - During mremap(), new_vma is often known to be placed after vma
114          *   in rmap traversal order. This ensures rmap will always observe
115          *   either the old pte, or the new pte, or both (the page table locks
116          *   serialize access to individual ptes, but only rmap traversal
117          *   order guarantees that we won't miss both the old and new ptes).
118          */
119         if (need_rmap_locks) {
120                 if (vma->vm_file) {
121                         mapping = vma->vm_file->f_mapping;
122                         i_mmap_lock_write(mapping);
123                 }
124                 if (vma->anon_vma) {
125                         anon_vma = vma->anon_vma;
126                         anon_vma_lock_write(anon_vma);
127                 }
128         }
129 
130         /*
131          * We don't have to worry about the ordering of src and dst
132          * pte locks because exclusive mmap_sem prevents deadlock.
133          */
134         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
135         new_pte = pte_offset_map(new_pmd, new_addr);
136         new_ptl = pte_lockptr(mm, new_pmd);
137         if (new_ptl != old_ptl)
138                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
139         arch_enter_lazy_mmu_mode();
140 
141         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
142                                    new_pte++, new_addr += PAGE_SIZE) {
143                 if (pte_none(*old_pte))
144                         continue;
145                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
146                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
147                 pte = move_soft_dirty_pte(pte);
148                 set_pte_at(mm, new_addr, new_pte, pte);
149         }
150 
151         arch_leave_lazy_mmu_mode();
152         if (new_ptl != old_ptl)
153                 spin_unlock(new_ptl);
154         pte_unmap(new_pte - 1);
155         pte_unmap_unlock(old_pte - 1, old_ptl);
156         if (anon_vma)
157                 anon_vma_unlock_write(anon_vma);
158         if (mapping)
159                 i_mmap_unlock_write(mapping);
160 }
161 
162 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
163 
164 unsigned long move_page_tables(struct vm_area_struct *vma,
165                 unsigned long old_addr, struct vm_area_struct *new_vma,
166                 unsigned long new_addr, unsigned long len,
167                 bool need_rmap_locks)
168 {
169         unsigned long extent, next, old_end;
170         pmd_t *old_pmd, *new_pmd;
171         bool need_flush = false;
172         unsigned long mmun_start;       /* For mmu_notifiers */
173         unsigned long mmun_end;         /* For mmu_notifiers */
174 
175         old_end = old_addr + len;
176         flush_cache_range(vma, old_addr, old_end);
177 
178         mmun_start = old_addr;
179         mmun_end   = old_end;
180         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
181 
182         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
183                 cond_resched();
184                 next = (old_addr + PMD_SIZE) & PMD_MASK;
185                 /* even if next overflowed, extent below will be ok */
186                 extent = next - old_addr;
187                 if (extent > old_end - old_addr)
188                         extent = old_end - old_addr;
189                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
190                 if (!old_pmd)
191                         continue;
192                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
193                 if (!new_pmd)
194                         break;
195                 if (pmd_trans_huge(*old_pmd)) {
196                         int err = 0;
197                         if (extent == HPAGE_PMD_SIZE) {
198                                 VM_BUG_ON_VMA(vma->vm_file || !vma->anon_vma,
199                                               vma);
200                                 /* See comment in move_ptes() */
201                                 if (need_rmap_locks)
202                                         anon_vma_lock_write(vma->anon_vma);
203                                 err = move_huge_pmd(vma, new_vma, old_addr,
204                                                     new_addr, old_end,
205                                                     old_pmd, new_pmd);
206                                 if (need_rmap_locks)
207                                         anon_vma_unlock_write(vma->anon_vma);
208                         }
209                         if (err > 0) {
210                                 need_flush = true;
211                                 continue;
212                         } else if (!err) {
213                                 split_huge_page_pmd(vma, old_addr, old_pmd);
214                         }
215                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
216                 }
217                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
218                                                       new_pmd, new_addr))
219                         break;
220                 next = (new_addr + PMD_SIZE) & PMD_MASK;
221                 if (extent > next - new_addr)
222                         extent = next - new_addr;
223                 if (extent > LATENCY_LIMIT)
224                         extent = LATENCY_LIMIT;
225                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
226                           new_vma, new_pmd, new_addr, need_rmap_locks);
227                 need_flush = true;
228         }
229         if (likely(need_flush))
230                 flush_tlb_range(vma, old_end-len, old_addr);
231 
232         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
233 
234         return len + old_addr - old_end;        /* how much done */
235 }
236 
237 static unsigned long move_vma(struct vm_area_struct *vma,
238                 unsigned long old_addr, unsigned long old_len,
239                 unsigned long new_len, unsigned long new_addr, bool *locked)
240 {
241         struct mm_struct *mm = vma->vm_mm;
242         struct vm_area_struct *new_vma;
243         unsigned long vm_flags = vma->vm_flags;
244         unsigned long new_pgoff;
245         unsigned long moved_len;
246         unsigned long excess = 0;
247         unsigned long hiwater_vm;
248         int split = 0;
249         int err;
250         bool need_rmap_locks;
251 
252         /*
253          * We'd prefer to avoid failure later on in do_munmap:
254          * which may split one vma into three before unmapping.
255          */
256         if (mm->map_count >= sysctl_max_map_count - 3)
257                 return -ENOMEM;
258 
259         /*
260          * Advise KSM to break any KSM pages in the area to be moved:
261          * it would be confusing if they were to turn up at the new
262          * location, where they happen to coincide with different KSM
263          * pages recently unmapped.  But leave vma->vm_flags as it was,
264          * so KSM can come around to merge on vma and new_vma afterwards.
265          */
266         err = ksm_madvise(vma, old_addr, old_addr + old_len,
267                                                 MADV_UNMERGEABLE, &vm_flags);
268         if (err)
269                 return err;
270 
271         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
272         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
273                            &need_rmap_locks);
274         if (!new_vma)
275                 return -ENOMEM;
276 
277         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
278                                      need_rmap_locks);
279         if (moved_len < old_len) {
280                 /*
281                  * On error, move entries back from new area to old,
282                  * which will succeed since page tables still there,
283                  * and then proceed to unmap new area instead of old.
284                  */
285                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
286                                  true);
287                 vma = new_vma;
288                 old_len = new_len;
289                 old_addr = new_addr;
290                 new_addr = -ENOMEM;
291         } else if (vma->vm_file && vma->vm_file->f_op->mremap)
292                 vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
293 
294         /* Conceal VM_ACCOUNT so old reservation is not undone */
295         if (vm_flags & VM_ACCOUNT) {
296                 vma->vm_flags &= ~VM_ACCOUNT;
297                 excess = vma->vm_end - vma->vm_start - old_len;
298                 if (old_addr > vma->vm_start &&
299                     old_addr + old_len < vma->vm_end)
300                         split = 1;
301         }
302 
303         /*
304          * If we failed to move page tables we still do total_vm increment
305          * since do_munmap() will decrement it by old_len == new_len.
306          *
307          * Since total_vm is about to be raised artificially high for a
308          * moment, we need to restore high watermark afterwards: if stats
309          * are taken meanwhile, total_vm and hiwater_vm appear too high.
310          * If this were a serious issue, we'd add a flag to do_munmap().
311          */
312         hiwater_vm = mm->hiwater_vm;
313         vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
314 
315         if (do_munmap(mm, old_addr, old_len) < 0) {
316                 /* OOM: unable to split vma, just get accounts right */
317                 vm_unacct_memory(excess >> PAGE_SHIFT);
318                 excess = 0;
319         }
320         mm->hiwater_vm = hiwater_vm;
321 
322         /* Restore VM_ACCOUNT if one or two pieces of vma left */
323         if (excess) {
324                 vma->vm_flags |= VM_ACCOUNT;
325                 if (split)
326                         vma->vm_next->vm_flags |= VM_ACCOUNT;
327         }
328 
329         if (vm_flags & VM_LOCKED) {
330                 mm->locked_vm += new_len >> PAGE_SHIFT;
331                 *locked = true;
332         }
333 
334         return new_addr;
335 }
336 
337 static struct vm_area_struct *vma_to_resize(unsigned long addr,
338         unsigned long old_len, unsigned long new_len, unsigned long *p)
339 {
340         struct mm_struct *mm = current->mm;
341         struct vm_area_struct *vma = find_vma(mm, addr);
342 
343         if (!vma || vma->vm_start > addr)
344                 goto Efault;
345 
346         if (is_vm_hugetlb_page(vma))
347                 goto Einval;
348 
349         /* We can't remap across vm area boundaries */
350         if (old_len > vma->vm_end - addr)
351                 goto Efault;
352 
353         /* Need to be careful about a growing mapping */
354         if (new_len > old_len) {
355                 unsigned long pgoff;
356 
357                 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
358                         goto Efault;
359                 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
360                 pgoff += vma->vm_pgoff;
361                 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
362                         goto Einval;
363         }
364 
365         if (vma->vm_flags & VM_LOCKED) {
366                 unsigned long locked, lock_limit;
367                 locked = mm->locked_vm << PAGE_SHIFT;
368                 lock_limit = rlimit(RLIMIT_MEMLOCK);
369                 locked += new_len - old_len;
370                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
371                         goto Eagain;
372         }
373 
374         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
375                 goto Enomem;
376 
377         if (vma->vm_flags & VM_ACCOUNT) {
378                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
379                 if (security_vm_enough_memory_mm(mm, charged))
380                         goto Efault;
381                 *p = charged;
382         }
383 
384         return vma;
385 
386 Efault: /* very odd choice for most of the cases, but... */
387         return ERR_PTR(-EFAULT);
388 Einval:
389         return ERR_PTR(-EINVAL);
390 Enomem:
391         return ERR_PTR(-ENOMEM);
392 Eagain:
393         return ERR_PTR(-EAGAIN);
394 }
395 
396 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
397                 unsigned long new_addr, unsigned long new_len, bool *locked)
398 {
399         struct mm_struct *mm = current->mm;
400         struct vm_area_struct *vma;
401         unsigned long ret = -EINVAL;
402         unsigned long charged = 0;
403         unsigned long map_flags;
404 
405         if (new_addr & ~PAGE_MASK)
406                 goto out;
407 
408         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
409                 goto out;
410 
411         /* Check if the location we're moving into overlaps the
412          * old location at all, and fail if it does.
413          */
414         if ((new_addr <= addr) && (new_addr+new_len) > addr)
415                 goto out;
416 
417         if ((addr <= new_addr) && (addr+old_len) > new_addr)
418                 goto out;
419 
420         ret = do_munmap(mm, new_addr, new_len);
421         if (ret)
422                 goto out;
423 
424         if (old_len >= new_len) {
425                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
426                 if (ret && old_len != new_len)
427                         goto out;
428                 old_len = new_len;
429         }
430 
431         vma = vma_to_resize(addr, old_len, new_len, &charged);
432         if (IS_ERR(vma)) {
433                 ret = PTR_ERR(vma);
434                 goto out;
435         }
436 
437         map_flags = MAP_FIXED;
438         if (vma->vm_flags & VM_MAYSHARE)
439                 map_flags |= MAP_SHARED;
440 
441         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
442                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
443                                 map_flags);
444         if (ret & ~PAGE_MASK)
445                 goto out1;
446 
447         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
448         if (!(ret & ~PAGE_MASK))
449                 goto out;
450 out1:
451         vm_unacct_memory(charged);
452 
453 out:
454         return ret;
455 }
456 
457 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
458 {
459         unsigned long end = vma->vm_end + delta;
460         if (end < vma->vm_end) /* overflow */
461                 return 0;
462         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
463                 return 0;
464         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
465                               0, MAP_FIXED) & ~PAGE_MASK)
466                 return 0;
467         return 1;
468 }
469 
470 /*
471  * Expand (or shrink) an existing mapping, potentially moving it at the
472  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
473  *
474  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
475  * This option implies MREMAP_MAYMOVE.
476  */
477 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
478                 unsigned long, new_len, unsigned long, flags,
479                 unsigned long, new_addr)
480 {
481         struct mm_struct *mm = current->mm;
482         struct vm_area_struct *vma;
483         unsigned long ret = -EINVAL;
484         unsigned long charged = 0;
485         bool locked = false;
486 
487         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
488                 return ret;
489 
490         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
491                 return ret;
492 
493         if (addr & ~PAGE_MASK)
494                 return ret;
495 
496         old_len = PAGE_ALIGN(old_len);
497         new_len = PAGE_ALIGN(new_len);
498 
499         /*
500          * We allow a zero old-len as a special case
501          * for DOS-emu "duplicate shm area" thing. But
502          * a zero new-len is nonsensical.
503          */
504         if (!new_len)
505                 return ret;
506 
507         down_write(&current->mm->mmap_sem);
508 
509         if (flags & MREMAP_FIXED) {
510                 ret = mremap_to(addr, old_len, new_addr, new_len,
511                                 &locked);
512                 goto out;
513         }
514 
515         /*
516          * Always allow a shrinking remap: that just unmaps
517          * the unnecessary pages..
518          * do_munmap does all the needed commit accounting
519          */
520         if (old_len >= new_len) {
521                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
522                 if (ret && old_len != new_len)
523                         goto out;
524                 ret = addr;
525                 goto out;
526         }
527 
528         /*
529          * Ok, we need to grow..
530          */
531         vma = vma_to_resize(addr, old_len, new_len, &charged);
532         if (IS_ERR(vma)) {
533                 ret = PTR_ERR(vma);
534                 goto out;
535         }
536 
537         /* old_len exactly to the end of the area..
538          */
539         if (old_len == vma->vm_end - addr) {
540                 /* can we just expand the current mapping? */
541                 if (vma_expandable(vma, new_len - old_len)) {
542                         int pages = (new_len - old_len) >> PAGE_SHIFT;
543 
544                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
545                                        vma->vm_pgoff, NULL)) {
546                                 ret = -ENOMEM;
547                                 goto out;
548                         }
549 
550                         vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
551                         if (vma->vm_flags & VM_LOCKED) {
552                                 mm->locked_vm += pages;
553                                 locked = true;
554                                 new_addr = addr;
555                         }
556                         ret = addr;
557                         goto out;
558                 }
559         }
560 
561         /*
562          * We weren't able to just expand or shrink the area,
563          * we need to create a new one and move it..
564          */
565         ret = -ENOMEM;
566         if (flags & MREMAP_MAYMOVE) {
567                 unsigned long map_flags = 0;
568                 if (vma->vm_flags & VM_MAYSHARE)
569                         map_flags |= MAP_SHARED;
570 
571                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
572                                         vma->vm_pgoff +
573                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
574                                         map_flags);
575                 if (new_addr & ~PAGE_MASK) {
576                         ret = new_addr;
577                         goto out;
578                 }
579 
580                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
581         }
582 out:
583         if (ret & ~PAGE_MASK)
584                 vm_unacct_memory(charged);
585         up_write(&current->mm->mmap_sem);
586         if (locked && new_len > old_len)
587                 mm_populate(new_addr + old_len, new_len - old_len);
588         return ret;
589 }
590 

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